Domestic water systems generally comprise separate hot and cold water piping, the hot water being heated in a hot water tank, both hot and cold water normally provided to a common mixed water delivery device (e.g. a faucet) in places such as baths, showers, and sinks. In normal use, the “turn-on” of such a mixed device by a consumer that wants water at a desired temperature includes the steps of:    a. waiting until the hot water arrives from the tank. This may take a while, in which time water is basically wasted. This waste is estimated to be on average about 10 liters (or more than 2 gallons) per turn-on;    b. adjusting the water temperature to a desired value in a process that includes trial (feeling the water temperature) and waiting until the water reaches that temperature; and    c. running the water even in cases when it is not needed, thus causing unnecessary waste.
A person taking a shower typically soaps him/herself while the water is running, and the same occurs for example during manual dishwashing. A faucet may be turned off while the water is not actually in use, but the majority of consumers do not do so, in order not to go through the “turn on” process again. Clearly, if one could temporarily turn off the flow of water and resume it instantly at the desired temperature, significant water and power savings could be attained.
A (partial) solution to the problem of waiting for hot water upon “turn-on” exists in hotels (but not normally in private homes). This solution consists of a circulation system that uses a double hot water pipe: the hot water pipe turns around and eventually returns to the hot water tank. Within the circle there is a small, preferably rotary pump that constantly circulates the hot water. The faucets are located close to a short mixed water pipe section that delivers water from the hot and cold pipes. Since at the entrance to this mixed pipe the water is always hot, when the faucet is turned on, the hot water arrives quite quickly. The disadvantages of this solution include a more expensive infrastructure (additional pipe to return the hot water) and waste of energy (both from the rotary pump which operates 24 hours a day, and from to continual leakage of heat from the hot water pipe to the surrounding environment). Obviously, this method is too expensive and energy-wasteful to be routinely applied in private homes.
The methods used in prior art for domestic hot water processing and delivery result in water and energy losses. It is thus desirable to provide devices, systems and methods that reduce these losses.